1. Field of the Invention
The present invention relates generally to an improved data processing system and in particular to a method and apparatus for preserving virtual file system information. Still more particularly, the present invention relates to a computer implemented method, apparatus, and a computer usable program product for preserving virtual file system information when a backup server takes over operations from a primary server.
2. Description of the Related Art
A network file system provides transparent remote access to file systems. Thus, two computers connected over a network can access each other's files in memory or stored on a storage device. Sharing of files can be restricted, such that only one computer can access the files of a second computer, or limitations can be placed on which files or directories can be accessed. An example of a network file system is NFS Version 4™, available from Sun Microsystems. In this network file system, and on other advanced network file systems, a virtual file system is maintained to provide a path from a root node to exported file systems.
In general, a file system provides a file “map” for a data processing system such that the data processing system can find requested files. File systems for individual data processing systems are often preserved on a hard disk drive. A virtual file system is a file system that is a file “map” of one or more remote computers and/or one or more local computers, singularly or together. Thus, a virtual file system can be a file “map” for an entire network of computers. A virtual file system is therefore also a reflection of one or more physical file systems. A virtual file system is, currently, stored in volatile memory, often of a network file system server.
In a high availability environment, one or more backup data processing systems are used to provide a safety net in case of failure of the primary data processing system or systems. For example, if the primary data processing system fails, then the one or more backup data processing systems can seamlessly take over operations formerly performed by the primary data processing system. If the primary data processing system is supporting a virtual file system in a network file system, then problems arise when transferring the virtual file system from the primary data processing system to the backup data processing system.
For example, either volatile file handles must be used or the file handles for the nodes of the virtual file system must be preserved during the transfer of operations from the primary data processing system to the backup data processing system. A file handle is a pointer to a data structure. Volatile file handles are file handles stored in a volatile memory.
Volatile file handles present a performance degradation to clients that access the backup data processing system. Unless the involved directories of the physical file system corresponding to the backup file system each have identical attributes, the file handles will not be saved or accessible. In practice, these file systems do not have identical attributes. Therefore, difficulties arise when transferring support of the virtual file system from a primary data processing system to a backup data processing system, which in part may defeat the purpose of the high availability backup data processing system.